Wentworth Lodge is a 210 bed fully accredited long-term
care facility, affiliated as a clinical teaching unit with the Faculty of
Health Sciences, McMaster University. Within the Lodge, there is a 47-bed
closed unit for residents with behavioural problems or wandering
tendencies: most, though not all, are demented. Residents in this unit are
younger (mean age 73-4 years on admission, versus 83-8 for other areas)
and physically healthier than residents in the rest of the Lodge. From
June to November, 1995, there was an outbreak of scabies on this ward,
which we were unable to control with any of the usual topical agents. All
residents were treated with crotamiton (July 7, 1995) and lindane (Aug 7,
1995). Several individuals with symptoms subsequently had repeated topical
applications of lindane and/or permethrin. Finally, on Nov 10, 1995, all
residents were treated with a single oral dose of ivermectin (150-200
µg/kg of body weight). Within 5 days, all rashes and symptoms had cleared
and no further treatment was needed.

Monthly number of deaths in ivermectin and control groups

Over the succeeding 6 months, there was a pattern of
excess deaths among the 47 residents who had received ivermectin. We
retrospectively constructed a 47-patient cohort of those who had not had
scabies for comparison purposes. We matched for age and sex the 47
patients who had received ivermectin with all other residents of the
Lodge. In every case in which there was more than one match, if one of the
matches died in the 6 months under study that resident was added to the
control cohort: ie, we deliberately maximised the number of deaths in the
comparison group. Between Nov 10, 1995, and May 10, 1996, 15 of the 47 who
had received ivermectin died, compared with five of the age-matched and
sex-matched cohort. The figure shows the time-course of deaths in the two
groups. Final causes of death showed no pattern, but ,hose in the
ivermectin group developed a sudden change in behaviour with lethargy,
anorexia, and listlessness which -receded death. Indeed, it was this
pattern that led us to study these deaths. These data, subjected to
Fisher's exact test, was significant to p=0.001, and
relative risk was 3.00 (95% CI 1.19-7.59).
We also analysed historical death rates for the 3-year period November,
1992, to November, 1995, compared with the 6-month period November, 1995,
to May, 1996:

The change in death rate is highly significant (p<0-0001 by both
chi-square and Fisher's exact tests).

Ivermectin has been used extensively in the past
against onchoceriasis and other tropical filarial diseases, with excellent
results and a low incidence of reported adverse effects." More recently,
ivermectin has been tested for the treatment of scabies in human beings."
-Mese reports were the basis on which the drug was used in our
institution. We suggest, in the face of what appears to be a significant
statistical association between use of ivermectin and increased risk of
death, that ivermectin should not be used for treatment of scabies in the
elderly, pending clarification of whether the association is causal. In
particular, confounding by an underlying medical condition or interaction
with another treatment (such as lindane or psychoactive drugs) needs to be
ruled out.